import pandas as pd
# 指定自定义索引
s2 = pd.Series([1.5, 2.8, 4.2], index=['a', 'b', 'c'])
print(s2)

print(s2.sum()) # 输出：8.5
print(s2.mean()) # 输出：2.833
print(s2.std()) # 输出：1.352
print(s2.cumsum()) # 输出累计和